X-ray screening diaphragm



Jan. 10, 1939.. N; G. SCHGNANDER El AL 2,143,799

X-RAY SCREENING DIAPHRAGM Filed Nov. 24, 19s"? Mel s Geo/g Sc/wzwwlefSven; Harald Ldll MMW Patented Jan. 10, 1939 UNITED. STATES X-RAYSCREENING DIAPHRAGM Nils Georg Schtinander and Sven Harald Ledin,Stockholm, Sweden Application November 24, 1937, Serial No. 176,352 InSweden November 28, 1936 8- Claims.

In order to absorb in fluoroscopy and X-ray photography undesirablesecondary rays emanating from the body to be examined, diaphragms forscreening or shutting out the secondary radiation are utilized. Thesediaphragms substantially consist of thin leaves standing upright andmade of a metal or a metal alloy opaque to the X-rays alternating withleavesof a material more transparent to the X-rays. These last-namedleaves may also consist of metal or a metal alloy, preferably of a lightmetal, such as for instance aluminium or magnesium or an alloycontaining these metals. The leaves opaque tothe X-rays may be made forinstance of lead, bismuth, gold, tungsten, tantalum, antimony, tin,silver, heavy platinum metals or of alloys which substantially consistof heavy metals. When in the following description the short expressionsheavy metal and light metal, respectively, are used, they are understoodto mean a metal or an alloy which permits X-rays to pass with difficultyor more easily.

This invention relates to, and it is the principal object thereof toprovide, an improved X-ray screening diaphragm of the characterdescribed. In the construction of diaphragms of this type, the lightmetal leaves and the heavy metal leaves preferably are metallicallyunited with each other to form a coherent body. Several methods ofmaking such screening diaphragms are already 3 known. It has, forinstance, been proposed to provide both sides of a light metal platewith a layer of a metal (soldering metal) having low melting point,whereafter one side of this plate is provided with a layer of heavymetal. This 35, plate is then cut into strips which are laid one uponthe other and the packet thus formed is subjected to pressure and heat,so that the heavy metal is metallically united with the light metalthrough the intermediary of the solderingmetal. 40 It has also beenattempted to dispense with the soldering metal and to unite the lightmetal directly with the'heavy metal.

These known methods, however, have certain drawbacks. As is well known,it is very difficult on account of the oxide layer, to solder lightmetals, especially aluminium. The joint between light metal andsoldering metal and between light metal and heavy metal, respectively,has come paratively feeble strength, so that diaphragms made accordingto the methods hitherto practiced may easily break to pieces.

The aforesaid drawbacks are eliminated according to the presentinvention by providing a new diaphragm construction and applying a newmethod of manufacture involving the following features:-Light metalplates or light metal ribbons are first provided with a metal coating, aso-called auxiliarycoating, having a surface which is solderable moreeasily than the light metal without consisting itself of easily meltable5, metal (soldering metal), whereupon the plates or ribbons or stripscut therefrom are metallicallyunited with each other after first havinginserted between them a layer or leaf of heavy metal and, if considerednecessary or desirable, some solderis); ing metal. Preferably, themelting point of the auxiliary coating metal is higher than that of theheavy metal. Further features of the invention will become apparent upona consideration of the detailed description of the various embodimentsthereof which follows.

In general, it will be preferable to cut the plates or ribbons intostrips which are metallically united with each other. It is, however,also possible to unite the whole plates to a block which 20 p form, sothat the diaphragm receives a circular 25.

form.

The advantage of the method according to the present invention istwofold. In the first instance, in making the diaphragm, one has nolonger to do with such a surface of the light metal, which is solderedor welded with difiiculty, but with the surface of a covering layer, theproperties with respect to easy soldering or welding of which may bechosen at Will and favourably. In the second instance, it is possible tochoose the coating metal in such manner that the joint between lightmetal and auxiliary layer on one hand and between the auxiliary layerand the heavy metal on the other hand has a considerably greaterstrength than a joint which is carried out directly between light metaland heavy metal or between light metal and soldering metal.

The auxiliary metal coating may be applied to the underlying metal byany suitable method which will assure an intimate adhesion of theauxiliary coating to the base metal, for instance by a mechanicalprocess, such as rolling, by an electro-galvanic process, or bysquirting molten metal onto the surface of the light metal.

In carrying out the electro-galvanic process for 50 covering the lightmetal plate with an auxiliary metal layer, the plate is carefullycleaned of all grease, after which it may also be pickled or dipped inorder to effect a rough surface. In this 'manner, strongly adheringgalvanic deposits may 55 be obtained, from all metals generally utilizedin electro-plating, such as' from copper, zinc, cadmium, iron, silver,etc. Especially, suitable for this purpose is nickel. The thickness ofthe nickel deposit should preferably be approximately 0.01 mm.

As is well known, pickling may be carried out in an alkaline bath or inan acid bath, for instance hydrochloric acid with metal salts. Acrystalline surface which is very favourable for the adhesion of theauxiliary metal coating is obtainedby pickling the plates or ribbonsseveral times, alternating in the alkaline bath and in the acid bath.

In some cases it may be of advantage to apply two auxiliary metalcoatings one on top of the other in order to assure the best possibleadhesion of the auxiliary coating to the light metal as well as to theheavy metal and to the soldering metal. When in the followingdescription mention is made of the melting point of the metal coating,always the melting point is meant of that partial coating which meltseasiest.

In case the heavy metal employed is a metal having a low melting point,such as for instance lead or a lead alloy, the plates or ribbons oflight metal which are provided with an auxiliary coating may be coatedwith the desired layer of heavy metal directly, for instance by dippingthe same into a bath of molten heavy metal. The diaphragm is then madeby joining strips coated with a layer of heavy metal alternately withstrips of light metal having one auxiliary coating only, and, ifdesired, soldering metal may be employed for fastening the strips toeach other. In this case, however, the thickness of the leaves of heavymetal will al ways be relatively small, and therefore, the method justmentioned will be applied substantially in such instances only wherevery thin heavy metal leaves are desired.

In general, however, methods will be preferred in which the heavy metalis introduced in the form of metal foils. According to one proposal, forinstance, light metal strips having an auxiliary metal coatingalternating with heavy metal strips may be laid one on top of the other,whereupon the pile of strips is compressed while simultaneously applyingheat and adding soldering metal to the edges of the strips. Thisprocess, however, has the disadvantage that the soldering metal, havingbeen added in a surplus quantity, forms, to a very extensive degree, analloy with the heavy metal, for instance lead, so that the heavy metalpartly melts away or by mixing itself with the soldering metal does noteffectively screen the secondary rays.

For this reason, it is preferred to apply the soldering meal before theheating process in a limited quantity between the strips to be united.This introduction of the soldering metal may be carried out by laying asoldering metal foil between two alternating strips of light metal andheavy metal. The best method, however, is to apply a soldering metallayer on one or both sides of the light metal strips or of the heavymetal strips or of all strips. It is not necessary to apply moresoldering metal than is absolutely required for effecting a reliablejoint nor to heat the compressed strips at a temperature which is higherthan the melting point of the soldering metal; it may even be suiiicientto apply heat which is somewhat lower than said melting point.

As solding metal, all metals or alloys may be employed which will adhereto the auxiliary coating as well as to the heavy metal, and the meltingpoint of which lies under that of the auxiliary coating and that of theheavy metal. In many cases, it is recommended to use tin or an alloy oftin and lead as the soldering metal.

In this latter case, the soldering metal layer is produced in thefollowing manner:-The light metal plate or ribbon having been coatedwith an auxiliary layer is either dipped into flux, such as zincchloride, and thereafter into a tin melt or a tin-lead melt, or tin isdeposited thereon by a plating process, or a tin foil or a tin-lead foilis applied or pasted to both sides of the coated light metal plate.

It is within the scope of the invention to apply the soldering metal byany other process than those suggested above.

According to a preferred method, the light metal plates or ribbons,having first been provided on both sides with an auxiliary coating andthen with a soldering metal layer on top of said coating, are providedon one or both sides with a heavy metal coating. This last-named coatingmay be produced in any convenient manher, for instance electrolyticallyor by squirting. A very effective and reliable method, however, is toproduce the heavy metal layer by pasting a heavy metal foil onto theprepared light metal strip. As adhesive, one preferably uses a solderingor flux means, such as resin or stearin. To ensure good adhesion of theheavy metal foil, the plates or ribbons together with the metal foilbetween them are rolled.

If the prepared light metal plates have a coating of heavy metal on bothsides, it is recommended, when joining together strips thereof, toinsert between two such strips a strip of light metal which also has anauxiliary metal coating on both sides and a soldering metal layer but noheavy metal coating.

The light metal strips have a thickness of about 0.2-0.4 mm.; theauxiliary metal and the soldering metal layers have each a thickness ofabout 0.01-0.02 mm.; and the heavy metal layers a thickness of about0.04-0.06 mm. In special cases other dimensions may be employed.

Referring now to the accompanying drawing, which for the sake ofclearness shows a diaphragm in exaggerated manner and not to scale, apreferred method of manufacture will be described by way of example.Fig. l is an interrupted section of three elements of a diaphragmaccording to the invention. Fig. 2 is a section through an entirediaphragm, but only light metal strips alternating with heavy metalstrips have been shown, the auxiliary coatings and the soldering metallayers having been left out for the sake of clearness. Fig. 3 is afragmentary section similar to that of Fig. 2 but differing from thelatter in that the light metal strips alternating with the heavy metalstrips are arrranged in converging relationship with respect to oneanother.

In carrying out the method, a plate of aluminium I having a thickness ofabout 0.3 mm. is degreased, pickled and scratched, then plated with alayer of nickel 2 of about 0.01-0.015 mm. thickness, and washed.Thereafter it is plated with a layer of tin 3 with a thickness of about0.01 mm., and again washed and dried. Upon one side of this preparedlight metal plate some adhesive is then squirted and on top of this alead foil-4 of about 0.05 mm. thickness is laid and rolled. Both sidesare thereafter oiled with stearin and the plate is cut into strips whichare formed into a pile. This pile is packed into a press cassette ofaluminium, compressed and heated to a temperature just above the eutetiopoint of the alloy between lead and the soldering metal. After finishingthe edges of this pile and cutting it to the desired size it issurrounded by a protective cover 5, Fig. 2, of aluminium. This cover mayconveniently be made of two thin aluminium sheets which are twice foldedtogether at the edges 6.

In the examples shown in Figs. 1 and 2, the leaves are arranged inparallel relationship. It is, however, possible and within the scope ofthe present invention to arrange the leaves opaque to X-rays in planeswhich converge relatively to each other so as to coincide with thedirections of radiation from the focal point of the Roentgen tube as isindicated in Fig. 3. In other words, when utilizing a diaphragmaccording to the present invention in a Roentgen apparatus, thescreening elements have the main extension of their section directedtowards the focus of the Roentgen tube.

What we claim is:-

1. An X-ray screening diaphragm consisting of strips of light metalcoated with a metallic layer having a surface which is more easilysolderable than the surface of the light metal, alternating with stripsof heavy metal.

2. An X-ray screening diaphragm consisting of strips of heavy metalalternating with strips of light metal coated with a metallic layerhaving a surface which is more easily solderable than that of the lightmetal and the melting point of which is higher than that of the heavymetal.

3. An X-ray screening diaphragm consisting of strips of heavy metalalternating with strips of light metal coated with a metallic layerhaving an easily solderable surface, and having a layer of solderingmetal applied to said surface.

4. An X-ray screening diaphragm consisting of leaves of lead alternatingwith leaves of aluminium which is coated with nickel and with tin on topof the nickel.

5. An X-ray screening diaphragm consisting of leaves of heavy metalalternating with leaves of light metal coated with a metallic layerhaving an easily solderable surface, said leaves being arranged inconverging relationship with respect to each other.

6. An X-ray screening diaphragm consisting of elements of heavy metalalternating with elements of light metal coated with a metallic layerhaving an easily solderable surface and having a higher melting pointthan said elements of heavy metal.

7. An X-ray screening diaphragm as claimed in claim 6, in which theelements of heavy metal and the elements of light metal are arranged inconverging relationship with respect to each other.

8. An X-ray screening diaphragm consisting of leaves of heavy metalstanding upright alternating with leaves of light metal also standingupright, and a plate of light metal mounted on either side of thediaphragm covering the short edges of the upright standing leaves.

NILS GEORG SCHGNANDER. SVEN HARALD LEDIN.

